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Of all two-dimensional semiconductor crystals, WSe2 is particularly interesting due to its sizable bandgap, high carrier mobility, and compatibility with large-scale synthesis. By passivating WSe2 MOSFETs with atomic-layer-deposited Al2O3, they are stable in room environment for more than five months. The passivation also increases their current capacity by two orders of magnitude. Their cutoff frequencies peak around room temperature, with the forward current cutoff frequency ${f} _{T} \sim 0.6$ GHz and the maximum frequency of oscillation ${f} _{{\textit {MAX}}} \sim 2$ GHz. These results show WSe2 is a promising material for gigahertz thin-film transistors. However, if the surface passivation is not optimized, fixed charge in the passivation layer may lead to temporal and temperature instabilities.

This article is the first report of MOSFETs fabricated on PtSe2 grown by molecular beam epitaxy. Both material synthesis and device fabrication are done below 450 °C—the thermal budget of CMOS back-end-of-line processes. The MOSFETs are batch-fabricated by a CMOS-compatible process on 200-mm-diameter Si substrates prepared by a state-of-the-art BiCMOS foundry. With three monolayers of PtSe2, an n-type MOSFET exhibits a current ON/OFF ratio of 43 at room temperature, which increases to 1600 at 80 K. These results are among the best of transistors based on synthesized PtSe2. Despite the thin PtSe2 layer, doping by contact bias lowers the contact resistance significantly and boosts the current capacity and the ON/OFF ratio. Temperature-dependent current-voltage characteristics imply a bandgap of approximately 0.2 eV, which confirms that the semiconductor-semimetal transition of PtSe2 is not as abrupt as originally predicted. Better MOSFET performance can be expected by growing even thinner PtSe2 uniformly and by thickening the PtSe2 in the contact regions.

Having a sizable band gap and high carrier mobility, black phosphorus (BP) is a promising two-dimensional material for high-frequency electronic and optoelectronic devices. Further, for metal-oxide-semiconductor field-effect transistors (MOSFETs) operating at high frequencies, they must have a top gate of submicron length instead of the commonly used global back gate. However, without the global back gate to electrostatically induce doping in BP, top-gated submicron BP MOSFETs have not reached their full potential mainly due to large contact resistances. Here, we report top-gated submicron BP MOSFETs with local contact bias electrodes to induce doping in the contact region. This resulted in reduced contact resistance and, in turn, orders of magnitude improvement in current capacity (500 μA/μm) and peak transconductance (40 μS/μm), if compared with top-gated BP transistors without any back-gating scheme. In turn, these improvements resulted in a forward current gain cutoff frequency of 37 GHz and a maximum frequency of oscillation of 22 GHz at room temperature, the highest reported for BP MOSFETs up to date.

Microwave performance of MOSFETs with a tellurene channel is reported for the first time. The measured forward current-gain cutoff frequency and the maximum frequency of oscillation are 1.4 GHz and 3.6 GHz, respectively. Overcoming the challenge for contacting 2D materials, source contact bias is shown to increase the drain current three times and the peak transconductance four times. Additionally, tellurene being stable in air, the MOSFETs are stable for months even without surface passivation. This suggests that tellurene is a viable candidate channel material for thin-film transistors capable of operation at microwave frequencies.

Wafer-scale fabrication of PtSe2 MOSFETs was demonstrated by photolithography on Pt films directly selenized at 400 °C. Taking advantage of the unique property of PtSe2 to transition from a semiconductor to a semimetal as its thickness increases beyond a few monolayers, channel recess was adapted for improving gate control while keeping the contact resistance below 0.01 $\Omega \cdot \text {cm}$ . The wafer-scale fabrication resulted in uniform device characteristics so that average instead of best results was reported. For example, the drain currents at ${V}_{\text {GS}} = -10$ V, ${V}_{\text {DS}} = -1$ V were $25~\pm ~5$ , 57 ± 8, and $618~\pm ~17~\mu \text{A}/\mu \text{m}$ for 4-, 8-, and 12-nm-thick PtSe2, respectively. The corresponding peak transconductances were 0.20 ± 0.1, 0.60 ± 0.05, and $1.4~\pm ~0.1~\mu \text{S}/\mu \text{m}$ . The forward-current cutoff frequency of 12-nm-thick PtSe2 MOSFETs was 42 ± 5 MHz, whereas the corresponding frequency of maximum oscillation was 180 ± 30 MHz. These results confirmed the application potential of PtSe2 for future-generation thin-film transistors.

Solution-processed 2-D materials, being low temperature, low cost, and scalable, are attractive for future-generation thin-film and flexible transistors. However, it is challenging to dispense solution-processed 2-D material into a thin and continuous channel for effective and uniform gate control. In addition, a thick channel under the source and drain contacts is required to increase the transfer length and decrease the edge contact resistance. To overcome such a dilemma and to obtain the optimum combination of effective gate control and low contact resistance, channel recess was demonstrated for the first time on MoS2, so that the channel is thin in the gate region but thick in the source and drain regions. Specifically, channel recess by CHF3/O2 dry etching up to 60 s was performed on submicron buried-gate MOSFETs fabricated on 20-nm-thick spin-coated MoS2. It was found that the channel recess improved the current on/off ratio by 3 orders of magnitude while maintaining approximately the same contact resistance and peak transconductance as that of a uniformly 20-nm-thick channel. The resulted performance was among the best of all solution-processed MoS2 MOSFETs. The same channel recess technique can be used to improve the performance of MOSFETs made of other solution-processed 2-D materials.

With novel contact and gate dielectric, a top-gated black phosphorus MOSFET exhibited record performance with 19-GHz forward-current-gain cutoff frequency and 29-GHz maximum frequency of oscillation. These results demonstrated the potential of two-dimensional atomic-layered materials for future-generation thin-film transistors capable of microwave operation. Further, analysis of the cutoff frequencies showed that the novel contact rendered contact resistance to secondary importance and, with improved transconductance, the black phosphorus MOSFET may even operate at millimeter-wave frequencies.

For the first time, thousands of RF MOSFETs were batch-fabricated on liquid-exfoliated Mos 2 below 300°C with nearly 100% yield. The large-scale fabrication with high yield allowed the average performance instead of the best performance to be reported. The DC performance of these devices were typical, but the RF performance, enabled by buried gates and on the order of 100 MHz, was reported for the first time for liquid-exfoliated Mos 2 . To resolve the dilemma of thin vs. thick films, channel recess was used on 20-nm thick films to improve the gate control while keeping the contact resistance lower than that on 10-nm films. These innovations may enable thin-film transistors to operate in the microwave range

For the first time, thousands of tellurene MOSFETs were batch-fabricated by a CMOS-compatible wafer process. However, the yield was only approximately 1% mainly because the tellurene was nonuniform and discontinuous. Nevertheless, the large-scale material-device correlation confirmed that the thicker the tellurene, the higher the current capacity, but the lower the on/off ratio. Such large-scale material/device correlation can help improve both the material and the device in the future.

Thousands of high-performance 2D metal-oxide-semiconductor field effect transistors (MOSFETs) were fabricated on wafer-scale chemical vapor deposited MoS2 with fully-CMOS-compatible processes such as photolithography and aluminum metallurgy. The yield was greater than 50% in terms of effective gate control with less-than-10 V threshold voltage, even for MOSFETs having deep-submicron gate length. The large number of fabricated MOSFETs allowed statistics to be gathered and the main yield limiter to be attributed to the weak adhesion between the transferred MoS2 and the substrate. With cut-off frequencies approaching the gigahertz range, the performances of the MOSFETs were comparable to that of state-of-the-art MoS2 MOSFETs, whether the MoS2 was grown by a thin-film process or exfoliated from a bulk crystal.

The design of subharmonic mixers is complicated and involves separation of signals and application of correct loading at idler frequencies. In this paper we propose an improvement to the novel generic approach, which was published by us earlier. The new method enables the designer to establish the optimum loading conditions for the different signals to achieve low conversion loss and good matching simultaneously. The main improvement compared to the "old" method is the ability to use the optimization option available in commercial microwave CAD to optimize the circuit performance, rather than using a manual tune option. Thus, the design can be fast and efficient. The method is demonstrated by a design example of a 60 GHz ×4 subharmonic mixer.

In this paper we present two topologies of QPSK (Quadrature Phase Shift Keying) Modulator for direct carrier modulation at 29.5 GHz for satellite communications using PIN technology. Previously published designs use PHEMT technology. PIN diodes allow operation at high power level (several watts at Ka band) and yield better switching performance compared to PHEMT switches. Our designs exhibit wide bandwidth (3GHz) and reasonable loss (5.5 db). In addition, we present a novel method for a self error correction QPSK modulator, which can yield high quality modulator at millimeter waves.

The GaAs MSM (Metal - Semiconductor - Metal) device is a very useful planar and MMIC compatible photodetector and electron-detector. We present here a newly identified secondary detection mechanism related to the interface between the semi-insulating substrate and the epitaxial layer. This new mechanism is characterized by a high detection gain but low speed. Experimental results are presented to verify the analysis, and possible applications are suggested by utilizing both the primary and secondary detection mechanisms.

A compact four-channels high gain and high isolation receiver unit has been developed at Ka-band frequencies. A total of 48 input and output signals are present in the receiver unit: 15 RF signals, 16 differential control signals and 5 DC bias feeds. The receiver unit presents 30dB insertion gain, 7.5dB noise figure and over 32dB isolation between the transmitter and receiver paths with an overall transmission insertion loss of 2dB.

A 2 Watt Ka-band MMIC power amplifier was designed using a ternary combination of power P-HEMT devices as a means to reduce the chip size. The three-staged amplifier exhibited a large signal gain of 12-15 dB over a bandwidth of 36-39 GHz. The design was very robust with RF/DC wafer yields of 60-70%.

This paper presents lumped elements equivalent circuits for several interconnects between microstrip and CPW transmission lines printed on GaAs and silicon substrates using flip chip technology. The effect of the bump height on the transition insertion and return losses and on the element values of the equivalent circuit is presented. It is shown that the performance of flip chip transitions is limited by the parasitic capacitance between the bump interconnects and the bump pads. By proper choice of the bump height, the area of the bump interconnects and the bump pads, it is possible to obtain bandwidth of the order of 150GHz.

The Signal Space approach [1],[2], which is an extension of Steer's [3] "Generalized Power Series" method, enables for a given nonlinearity, a direct calculation of the current spectrum given the voltage spectrum. This approach is suited to the implementation for harmonic balance which is today the most useful approach for nonlinear microwave network analysis [4],[5]. In this paper we propose analytical design tool for oscillators using the Signal Space approach. The expressions for oscillator parameters such as oscillation frequency, stability conditions, power output, injection locking bandwidth etc., were applied in the design of a X band Gunn microstrip oscillator in the MATLAB program. The stability condition expression is compatible with Kurakawa's results, and the injection locking bandwidth calculation includes Adler's expression as a limiting case. There is good agreement between the simulation and the measurement results.

This paper describes the design and performance of a new compact and low cost Transmitter for Ka band VSAT satellite communication ground terminal. The main features of the transmitter are: 32.5dBm minimum output power for ?16 dBm input power over the frequency range of 27.5-31GHz. The Transmitter consists of low power MMIC amplifier, band pass filter, a medium power MMIC amplifier, a four way microstrip power divider, a high power module with four MMIC power amplifiers, a four way waveguide power combiner and DC supply unit. The Transmitter size is 15.5×11×2.5 cm and weighs less than 0.6 Kg.

In this paper we present an RF front end prototype for the newly emerging Ka band VSAT satellite communications networks. This front end is being developed as an effort to establish low cost technology base for future VSAT networks operating in the 30/20 GHz band. The front-end reported here is the first laboratory prototype intended to establish a proof of performance. An engineering prototype is being developed presently with emphasize on low cost. The main features of the new front end are: 32 dbm transmit power over the range 27.5-31 GHz, -20dbm input power at the transmit IF band of 4.5-8 GHz, 3.5 db noise figure over the band 17.7-21.2 GHz, Receive IF band: 6.2-9.7 GHz. A single source at 11.5 GHz is used as the common LO for both transmit and receive units. To our knowledge, units like the one described here are not available commercially.

FMCW sensors are gaining more importance-in a wide variety of applications for measuring target range and relative velocity. In order to improve resolution of the sensor for measuring between two close, adjacent targets, one has to widen the bandwidth and to improve the linearity of the transmit chirp. In addition, improving the linearity increases the signal to noise ratio, and thus, the receiver sensitivity. In this paper we present a new analog, closed loop system, which pins the higher order VCO nonlinearity resulting in an overall linearity of 0.1%. The system is compact, cheap to implement, and free from spurious signals. Our theoretical analysis also identifies the important parameters which influence the linearity and sensitivity of the receiver.

Harmonic balance is today the most useful approach for nonlinear microwave network analysis. Usually FFT is used to convert the nonlinear elements time waveforms into the frequency domain as part of the harmonic balance process. This approach is straight forward for a single frequency. excitation, but is quite complicated and time consuming for the multi-frequency excitation case. Steer [1] proposed the Generalized Power Series, which enables for a given nonlinearity a direct calculation of the currents spectrum given the voltages spectrum. In this paper we propose a mathematical model termed Signal Space, which is similar to Steer's approach but better suited to implementation for harmonic balance. In [2] we extracted the signal space and made an approximation between the harmonic currents subspaces to enable a treatment of high nonlinearity of elements. Under describing function criteria we use the Signal Space approach to get expressions for oscillator parameters such as oscillation frequency, stability condition, injection locking bandwidth etc. Our results are compatible with Kurakawa's expressions.

A novel approach for designing actively matched laser drivers on MMICs is presented here. The key elements of this approach are to optimize the active matching network of the driver in order to provide good input matching, to maximize the electrical-to-optical transfer function, and also to compensate the frequency response of the laser diode junction current. This provides a flat frequency response in the bandwidth of interest. This approach is demonstrated by design of a 1-4 GHz laser driver.